The present invention relates to echo detection stations such as Radar for mobile object direction, range, and velocity determination, and particularly to auxiliary identification equipment at such stations and also on cooperating or friendly mobile objects for identification friend or foe (IFF). Since mobile objects often include a radar station, and fixed stations may require identification to avoid attack by friendly equipped objects, each may involve both detection and IFF operation.
Many variations of such auxiliary equipment have been used. Wolff U.S. Pat. No. 2,885,665 illustrates a mere coded keying of a passive reflector or re-radiator for the actual radar signals, thus varying echo amplitude on radar display. The prearranged coding minimizes analysis of the signal and synthesis of a false signal by the enemy. Charrier U.S. Pat. No. 2,453,970 illustrates a coded and substantially delayed active re-transmitter, thus providing an additional delayed echo on radar display. Because of the wide variety of basic radar equipments, in many frequency bands, it has been common to provide with each radar auxiliary low power transmitters all on one IFF frequency unrelated to the radar. Actually IFF re-transmission may use another frequency, and coding may be used both ways, to minimize jamming as well as false reply from enemy objects.
It will be helpful to recognize certain IFF terms:
Transponder on objects, an active re-transmitter, as in Charrier and common IFF;
Responder on object, a term here used for the alternative passive re-radiator, as in Wolff;
Responsor at station, an accepted by somewhat inapt term for common IFF receiver, here replaced by receiver-processor, to emphasize the distinction from the term Responder as used above;
Interrogator at station, an IFF transmitter as in common IFF, sometimes applied to Radar transmitter also.